Multiple bonds in Be and B compounds

Bond lengths in all the boron trihalides are shorter than expected for single bonds, so the partial double bond character predicted seems reasonable in spite of the formal charges. Molecular orbital calculations for these molecules support significant double bond character. On the other hand, they combine readily with other molecules that can 

Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, England, 1984, pp. 412, 1047.) 

Molecule Atom Formal Charge Atom Formal Charge Expanded to  

FIGURE 3.6 Formal Charge and Expanded Electron Counts on Central Atom. 

Because of this tendency, boron trihalides are freqnently drawn with only six electrons around the boron. 

Other boron compounds that cannot be adequately described via simple electron-dot structures include hydrides such as B2H5, and many more complex molecules. Their structures are discussed in Chapters 8 and 15. 

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